Oleo-pneumatic shock absorber

ABSTRACT

A two-stage oleo-pneumatic shock absorber incorporating two pneumatic (air) pressure chambers, a high air pressure chamber and a low pressure (air) chamber, separated by a hydraulic fluid (oil) pressure chamber. The oil chamber contains an orifice and metering pin, which orifice and metering pin control the rate of collapse of the low pressure air chamber. It also contains a second orifice and metering pin which control the rate of collapse of the high pressure air chamber. Both metering pins are preprogrammed so as to interact with each other and effect a nearly constant load throughout the stroke of the shock absorber, even under transient loading conditions.

[1 1 3,724,832 Apr. 3, 1973 [54] CLEO-PNEUMATIC SHOCK PrimaryExaminer-James B. Marbert Attorney-Robert E. Geaque ABSORBER Frank Z.Ceska, Montreal, Canada [57] ABSTRACT A two-stage oleo-pneumatic shockabsorber incor- [75] Inventor:

'[73] Assignee: Menasco Manufacturing of Canada,

Ltd"Quebec Canada porating two pneumatic (air) pressure chambers, a Mar.9, 1971 high air pressure chamber and a low pressure (air) chamber,separated by a hydraulic fluid (oil) [22] Filed:

pressure [21] APPL 122,421 chamber. The oil chamber contains an orificetering pin, which orifice and metering pin control the and merate ofcollapse of the low pressure air chamber. It also contains a secondorifice and-metering pin which control the rate of collapse of the highpressure air chamber. Both metering pins are preprogrammed so R 8 0 4 W6W M m u6 MR "4 6 l 7 n6 "2 Ya mm ""8 S an Siam 0 cl UhF 1]] 2 8 5 55 [[las to interact with each other and effect a nearly con- [56] ReferencesCited 7 I stant load throughout the stroke of the shock ab- UNITEDSTATES PATENTS sorber, even under transient loading conditions.

12 Claims, 3 Drawing Figures 3,533,613 10/1970Bendicsen...........................267/64 R 3,265,381 8/1966 Katz et al....267/64 A CLEO-PNEUMATIC SHOCK ABSORBER BACKGROUND OF THE INVENTIONThis invention relates to shock absorbers and particularly to shockabsorbers of the oleo-pneumatic type wherein a novel overload relief isprovided which enhances the working characteristics of the shockabsorber. Shock absorbers of this general type are known and have provedto function particularly well for use in the shock strut of an aircraft.A shock absorber of this type is disclosed in U.S. Pat. No. 2,959,410and in pending U.S. patent application Ser. No. 812,652 whichapplication is assigned to the assignee of this application.

A requirement of all aircraft shock absorbers is that they absorb ordissipate the energy of descent or transient or vertical shocks withouttransferring them to the vehicle or aircraft structure. To this end,this type of shock absorber has previously been provided with either aspring-loaded or a pneumatically loaded relief valve which vents oilwhen excessive fluid pressure is created in an oil chamber of the shockabsorber. Such type relief valves, though, are limited in the magnitudeof transient loads and conditions they are capable of handling. In someload conditions, as for example, loads encountered by an aircraft inlanding on unprepared landing sites, this type of valve is inadequate todissipate the shocks encountered in landing without transferring them tothe aircraft structure.

It has therefore been an objective of this invention to provide anoleo-pneumatic shock absorber which is capable of handling the types oftransient loads and shocks encountered by an aircraft landing gear shockabsorber in the course of landing on unprepared landing sites.Unprepared landing sites are those which have obstacles, as, forexample, tree stumps and pot holes. Such a shock absorber must becapable of effectively reducing transient dynamic loads which resultfrom high velocity of descent together with impact or shock loads.Otherwise expressed, it has been an objective of this invention toprovide a shock absorber of the oleo-pneumatic type which is capable ofabsorbing the energy of impact during landing on unprepared landingsites without transferring heavy impact and transient loads whiletraversing obstacles through the landing gear to the aircraft structure.

These objectives are achieved and this invention is predicated upon theconcept of a two-stage shock absorber with a high pneumatic pressurechamber and a low pneumatic pressure chamber separated by a hydraulicchamber together with two preprogrammed metering pins for controllingthe rate of movement of the stroke of the shock absorber under varyingdynamic load conditions. One metering pin acts on the first stage of theshock absorber and the other acts upon the second stage. The profiles ofthe metering pins are preprogrammed so as to give a nearly constant loadthroughout the complete stroke of the gear under all types of landingconditions including those encountered when the landing gear strikesobstacles during touchdown and taxiing.

The second stage metering pin is so configurated that prior to fullcompression of the shock absorber the metering pin opens fully thesecond stage orifice to allow oil to dump and thus decrease the shockabsorber load. The load thus decreases so that there is still somestroke available to prevent the shock absorber from bottoming.

The primary advantage of this shock absorber is the ability of the shockabsorber to respond and maintain an even load condition on the aircraftwithout transferring high transient loads to the aircraft structureunder severe dynamic conditions which would have caused prior shockabsorbers to fail or bottom and transfer the load to the aircraft. Thisshock absorber also has the advantage of having minimal weight and ofbeing capable of very rapid dynamic response to severe transient loadconditions. 7

Other objects and advantages of this invention will become more apparentfrom the detailed description of the drawings in which:

FIG. 1 is a longitudinal cross section view of a shock absorberincorporating the invention of this application with the shock absorberillustrated in a fully extended or unloaded position.

FIG. 2 is a cross sectional view similar to FIG. 1 but .illustrating theshock absorber in a fully collapsed condition.

FIG. 3 is a diagram graphically illustrating the dynamic loadcharacteristics of the shock absorber of this invention.

Referring first to FIG. 1, there is illustrated a shock absorber 5 ofthe oleo-pneumatic type incorporating the invention of this application.This shock absorber 5 is adapted to be placed between the sprung massand the unsprung mass of a vehicle, more particularly, between thelanding gear and an aircraft structure.

Specifically, this shock absorber is intended to be used in connectionwith the landing gear of an aircraft which is capable of landing. on andtaking off from unprepared fields, as, for example, a field whichcontains tree stumps or pot holes.

The shock absorber 5 illustrated in FIG. 1 is shown in an extended oruncompressed condition. It consists of a cylinder 10 which is closed atits upper end by a closure cap 11. This cap is threaded onto the top ofthe cylinder, as indicated at 12, or is an integral part of thecylinder. A hollow filling tube 13 extends axially through the cap 11and is threaded into the cap as indicated at 14. This tube is closed bya threaded plug 15. There is a seal 16 between the tube 13 and theclosure cap 11.

An annular floating piston 18 is slidably mounted over the filler tube13 so that the filler tube acts as a guide rod for the piston. Thispiston 18 has a cylindrical hub section 19 on the top and a contouredsecond stage metering pin section 20 extending downwardly from thebottom of the piston 18. An O-ring seal 21 is located between theperiphery of the piston 18 and the inside surface 22 of the cylinder 10.Another O-ring seal 23 is located between the piston and the externalsurface 24 of the filler tube 13. Fluid passageways or openings arelocated at the bottom of piston head 18.

The closure cap 1], cylinder 10 and the top surface of the piston 18together with the filler tube 13, define an air pressure chamber 30. Airunder pressure, as, for example, 1600 pounds per square inch pressure,is admitted into the chamber through a filler tube 32 in the cap 11 Apressure gauge 34 extends through the cap 11 and enables the pressure inthe chamber 30 to be visually determined and inspected. Pressure in thechamber 30 normally biases the piston 18 downwardly against the topsurface 35 of an orifice plate 36 secured to the top of a first stagemetering pin 37. This metering pin 37 and the attached orifice plate 36are fixedly mounted on the interior of the cylinder and are held inplace in the cylinder by a locating ring 38. An annular flange orprotrusion 39 extends inwardly from the plate 36 to define an axialorifice 40 for a second metering pin 20.

The first stage metering pin 37 is hollow and extends downwardly fromthe orifice plate 36. It is closed at the bottom, as indicated at 42,and is externally contoured or shaped into a noncylindricalconfiguration, as indicated at 43. Holes or apertures 44 in the sidewall of the metering pin 37 connect the interior chamber 45 of the firststage metering pin '37 to a second stage oil chamber 46. 7

An axially movable annular piston head 50 is telescoped into thecylinder 10. A piston rod or piston tube 51 extends downwardly from thepiston 50 and defines a chamber for a floating piston 52. The chamber isclosed'at the bottom by a section 65 of a lug 71.

The floating piston 52 separates and divides the interior of the pistontube 51 into a first stage 'orlow pressure air chamber 53 and an oilpressure chamber 54. An O-ringseal 55 around the periphery of thefloating piston 52 prevents the leakage of air around the piston. Air isinjected into the first stage 'or low. pressure chamber 53 through aconventional air' valve 74. Generally,.the air pressure in this chamberis maintained at a lower pressure than that maintained in the upperpressure chamber 30. 1

There may be fixed orifices 56 extending through the piston 50.'Theseorifices 56 cooperate with rebound rings 57 to control the-rate ofreturn or extension of the shock absorber after it has been compressed.

An annular plug 60 is threaded into the bottom of the cylinder 10.-Theinner surface 61 of this .plug defines the sliding surface for thepiston tube 51. O-ring seals 62 and 63 prevent leakage of oil from achamber 64 located between the inside 22 ofthe cylinder 10 and theoutside of the tube 51.

The lower lug 71 is so configurated as to enable it to be connected tothe wheel of an aircraft. Two additional arms 72 and T73 are'integralwith or connected to the top of the cylinder 10 so as to enable the topof the cylinder to be connected or attached to the aircraft structure.Where so connected, the shock absorber 5-.

acts as a shock strut between the wheels and aircraft structure.

Oil or hydraulic fluid is injected intothe shock abs'orb'erthrough thefiller tube '13 by removing the plug 15 and pouringt-he oil throughthetube and into the chamber 54; The oil passes through orifices44andfills the upper chamber. 46 aroundthe first stage metering pin 37 andthe lower chamber 54 beneath the metering- OPERATION During the landingof the aircraft, the load or force is applied to the lower end of theshock absorber or to the lug 71', causing the piston 50 to telescopeinto cylinder 10, as is illustrated in FIG. 2. As the piston 50 movesupwardly into the chamber 46, it causes an increase in the oil pressurein the oil chamber 46. Fluid then flows from the high pressure chamber46 to the low pressure chamber 54 through orifice 48 in the piston. Therate at which it flows from the high pressure chamber to the lowpressure chamber is determined by the undulating tom of the chamber 53.Thereafter, continuedlo'ading' causes the pressure on'the oil in chamber45 to be transmitted through the apertures 44 and orifice 40 into theoil chamber 47 located beneath'the piston 18. The piston 18 then movesupwardly as the high pressure air in chamber 30 is compressed.

Static or slow loading conditions: as described hereinabove, aregraphically illustrated by the lower line 84' or line ABC of theload-stroke graph of FIG. 3. The portion-of AB of line 84 indicates theportion of the load-stroke curve required for full compression of thefirst stage air chamber 53. The portion BC indicates the load-strokecurve which occurs during the continued loading of the shock absorberduring the compression of the secondstage air chamber-30. To obtainthis. curve, though, the .load must be applied .very slowly.' v 1Dynamic response'of the-shock-absorber of this invention follows adifferent curve, the curve of the line 85 in FIG. 3., This curveis theresultof the interaction of the'oil passing through the meteringorifices 48 and 40 and the associated metering pins which generates andmaintains a relatively flat load curve AC (line 85).

When the landing wheel contacts a rough area such as a stump in alanding surface, a sharp sudden transient load is applied to the landinggear tire or tires.

As an example, after touchdown of the aircraft', the oil pressure: inthe chamber 46 quickly builds up and reaches the second stagecompression pressure of chamber 30.. At this point (which may occur atany stroke position) the second stage floating piston 18 and theattached second stage meteringpin 37 start-to move awayfrom the originalposition'depicted in FIG. 1, thereby allowing increased oil flowthroughthe second stage metering orifice 40. This second stage damping combinedwith the first stage damping which occurs as a result of the oil flowthroughout the orifice 48 is preprogrammed soasto give a nearly constantload (as indicated by the flat-portion of theline'85) in the shockabsorber throughout the complete stroke.

If an obstacle, as, for example, a tree stump, is encountered during thelanding impact, a'faster movement or increased rate of movement of theshock absorber occurs. At the same time, the second stage float! ingpiston 18 and attached metering pin 20 move further toward the fullycompressed position illustrated in FIG. 2. A sharp effective orificesize increase then occurs as a result of the tapered configuration ofthe end portion 25 of the metering pin 20, which increase in orificesize allows more oil to flow through the orifice and further collapsethe shock absorber. This increased flow represents overload relief orso-called load dumping. Under these circumstances the load through theshock absorber does not build up but 1 rather decreases. As shown on theload stroke diagram portion DC of the line 85, the load descends ordecreases to meet the second stage air spring curve line BC at point C.At this position, where the two curves ABC and ADC meet, some stroke isstill available for situations when an obstacle is contacted duringmaximum loading of the shock absorber. This remaining stroke thenprovides for situations which previously had no solution and would havebottomed prior art shock absorbers and transferred high transient loadsto the aircraft structure.

The programming of the two metering valves is controlled by the size ofthe orifices 40 and 48 and the contours of the metering pins and 37.Since the two pins are interacting, their functions must bepreprogrammed, preferably through analog representation so as to givethe required dynamic characteristics of the shock absorber. As analternative to the utilization of computer runs to test parameterchanges for the orifice size and metering pin contours, experimentaltest runs utilizing different configurations may be utilized to obtainoptimum configuration and load absorption characteristics.

The primary advantage of this invention resides in the ability of theshock absorber to absorb repeated high transient loads. The second stagemetering pin does not simply open and dump the second stage oil pressureto the lower pressure chamber but opens at a controlled rateinter-related to the load and the flow then occurring through the firststage metering valve. This feature enables the shock absorber to handletransient loads which prior landing gear shock absorbers were incapableof handling. Therefore, the shock absorber enables aircraft to be landedover surfaces which have heretofore been considered too rough to permitsafe landing.

While I have described only a single embodiment of my invention, personsskilled in the art to which this invention pertains will readilyappreciate numerous changes and modifications which may be made withoutdeparting from the spirit of my invention. Specifically, additional airchambers may be added to the shock absorber to enable it to absorb stillgreater loads and to change the load-stroke curve. Additionally, theconfiguration and shape of the metering pins may be altered to obtaindifferent load-stroke curve characteristics. Therefore, I do not intendto be limited except by the scope of the appended claims.

Having described my invention, 1 claim:

1. A shock absorber comprising a cylinder having av hydraulic chamberseparated into sections by a movable piston;

first orifice means comprising a first stage preprogrammed meteringvalve and a first orifice, one of which is movable with said piston andthe other being fixed to said cylinder;

a compressible high pressure chamber operatively connected to saidhydraulic chamber through a second piston and capable of being changeddimensionally in response to movement of said second piston;

said second piston being in communication with said hydraulic chamber onone side thereof;

means for effecting relative movement between said first stage valve andsaid first orifice in response to application of a load to said piston,the improvement which comprises;

second orifice means comprising a second orifice in said chamber and asecond stage preprogrammed metering valve, one of which is fixed to saidcylinder and the other being movable with said second piston, saidsecond piston being movable in response to the pressure between saidsecond orifice and said second piston for controlling the rate ofcompression of said high pressure chamber whereby an increase inpressure in the hydraulic chamber caused by a high pressure transientload is instantaneously and simultaneously damped by the interaction ofthe flow of the hydraulic fluid through the two orifices and about thetwo metering valves and the resulting compression of the high pressurechamber.

2. In a shock absorber as defined in claim 1 having a low pressurecompressible chamber operatively connected -to said hydraulic chamber onthe other side thereof from said high pressure chamber and capable ofbeing changed dimensionally in response to movement of said firstpiston, said low pressure chamber being divided from said hydraulicchamber by a third piston whereby an increase in pressure in thehydraulic chamber caused by a hydraulicpressure transient load resultsin compression of the low pressure chamber.

3. A shock absorber means as defined in claim 1 wherein said secondorifice means comprises a second orifice in a plate fixed to saidcylinder, said .second stage metering valve being attached to'saidsecond piston.

4. A shock absorber as defined in claim 2 wherein said high pressure andsaid low pressure chambers comprise air spring means.

5. The shock absorber as defined in claim 1 in which said second stagepreprogrammed metering valve is programmed such that it opens fully todump hydraulic fluid from said hydraulic chamber prior to fullcompression of said shock absorber such that the load transmittedthrough said shock absorber decreases dur-. ing the last portion of thestroke of the shock absorber.

6. A shock absorber comprising a cylinder having a cation of a load tosaid plate, the improvement which comprises;

a second orifice plate fixed in said hydraulic chamber A shock absorberdefined in'claim 6 having low pressure chamber on the opposite end ofsaid hydraulic chamber from said high pressure chamber, said lowerpressure chamber being sealingly separated from said hydraulic chamberby a second piston slideably mounted in said cylinder so that a changein pressure in said chamber is damped by the compression of said lowpressure chamber.

8. The shock absorber as defined in claim 6 in which said second stagepreprogrammed metering pin is programmed such that it opens fully todump hydraulic fluid from said hydraulic chamber prior to fullcompression of said shock absorber such that the load transmittedthrough said shock absorber decreases during the last portion of thestroke of the shock absorber.

9. The shock'absorber as defined in claim 6 wherein said first meteringpin' is generally hollow and said second metering pin extends into thehollow interior of said first metering pin.

10. The shock absorber as defined in claim 7 in which both said highpressure and said low pressure chambers comprise air spring means.

1 1. The shock absorber as defined in claim 6 wherein both said firstand second metering pins have noncylindrical external contours.

12. The shock absorber as defined in claim 9 wherein said first meteringpin contains flow openings connecting the hollow interior of said pin tosaid hydraulic chamber.

1. A shock absorber comprising a cylinder having a hydraulic chamberseparated into sections by a movable piston; first orifice meanscomprising a first stage preprogrammed metering valve and a firstorifice, one of which is movable with said piston and the other beingfixed to said cylinder; a compressible high pressure chamber operativelyconnected to said hydraulic chamber through a second piston and capableof being changed dimensionally in response to movement of said secondpiston; said second piston being in communication with said hydraulicchamber on one side thereof; means for effecting relative movementbetween said first stage valve and said first orifice in response toapplication of a load to said piston, the improvement which comprises;second orifice means comprising a second orifice in said chamber and asecond stage preprogrammed metering valve, one of which is fixed to saidcylinder and the other being movable with said second piston, saidsecond piston being movable in response to the pressure between saidsecond orifice and said second piston for controlling the rate ofcompression of said high pressure chamber whereby an increase inpressure in the hydraulic chamber caused by a high pressure transientload is instantaneously and simultaneously damped by the interaction ofthe flow of the hydraulic fluid through the two orifices and about thetwo metering valves and the resulting compression of the high pressurechamber.
 2. In a shock absorber as defined in claim 1 having a lowpressure compressible chamber operatively connected to said hydraulicchamber on the other side thereof from said high pressure chamber andcapable of being changed dimensionally in response to movement of saidfirst piston, said low pressure chamber being divided from saidhydraulic chamber by a third piston whereby an increase in pressure inthe hydraulic chamber caused by a hydraulic pressure transient loadresults in compression of the low pressure chamber.
 3. A shock absorbermeans as defined in claim 1 wherein said second orifice means comprisesa second orifice in a plate fixed to said cylinder, said second stagemetering valve being attached to said second piston.
 4. A shock absorberas defined in claim 2 wherein said high pressure and said low pressurechambers comprise air spring means.
 5. The shock absorber as defined inclaim 1 in which said second stage preprogrammed metering valve isprogrammed such that it opens fully to dump hydraulic fluid from saidhydraulic chamber prior to full compression of said shock absorber suchthat the load transmitted through said shock absorber decreases duringthe last portion of the stroke of the shock absorber.
 6. A shockabsorber comprising a cylinder having a hydraulic chamber separated intosections by a movable piston Orifice plate; a first stage preprogrammedmetering pin fixed within the hydraulic chamber and passing through theorifice in said plate; a high pressure chamber on one side of saidhydraulic chamber being sealingly separated from said hydraulic chamberby a first piston slideably mounted in said cylinder and located at oneend of said hydraulic chamber; means for effecting movement of saidplate relative to said first stage metering pin in response toapplication of a load to said plate, the improvement which comprises; asecond orifice plate fixed in said hydraulic chamber and a second stagepreprogrammed metering pin secured to said first piston and passingthrough the orifice in said second plate, said second stage metering pinbeing movable relative to said orifice of said second orifice plate inresponse to a pressure change in said chamber for controlling the rateof compression of said high pressure chamber whereby an increase inpressure in the hydraulic chamber caused by a high pressure transientload is instantaneously damped by the interaction of the flow ofhydraulic fluid through the two orifices and about the two meteringpins.
 7. A shock absorber defined in claim 6 having a low pressurechamber on the opposite end of said hydraulic chamber from said highpressure chamber, said lower pressure chamber being sealingly separatedfrom said hydraulic chamber by a second piston slideably mounted in saidcylinder so that a change in pressure in said chamber is damped by thecompression of said low pressure chamber.
 8. The shock absorber asdefined in claim 6 in which said second stage preprogrammed metering pinis programmed such that it opens fully to dump hydraulic fluid from saidhydraulic chamber prior to full compression of said shock absorber suchthat the load transmitted through said shock absorber decreases duringthe last portion of the stroke of the shock absorber.
 9. The shockabsorber as defined in claim 6 wherein said first metering pin isgenerally hollow and said second metering pin extends into the hollowinterior of said first metering pin.
 10. The shock absorber as definedin claim 7 in which both said high pressure and said low pressurechambers comprise air spring means.
 11. The shock absorber as defined inclaim 6 wherein both said first and second metering pins havenoncylindrical external contours.
 12. The shock absorber as defined inclaim 9 wherein said first metering pin contains flow openingsconnecting the hollow interior of said pin to said hydraulic chamber.